A case of prenatally detected cri du chat syndrome (5p-) is reported. Amniocentesis was performed following an abnormal ultrasound finding of isolated moderate bilateral ventriculomegaly. The karyotype showed a terminal deletion of the short arm of chromosome 5 including the critical region 5p15 for cri du chat syndrome. This was confirmed by fluorescence in situ hybridisation (FISH). Isolated mild ventriculomegaly may be a non-specific marker for cri du chat syndrome.